Pi'ototheca of the Madreporaria, 19 



forms. Fig-. 13 h, liowever, Is of very great morpliological 

 interest and demands some further attention. 



In tlie first place, it sliou's a simple and very efficient 

 method of enabling- the skeleton to stand upright. It differs 

 from the radicle-formation in that the lip bends over all round. 



The septa which come over the lip run down on the outside 

 just as we know that they run down inside tlie radicle (see 

 fig. 8 h). It is also obvious that the flesh of the polyp must 

 have clothed the outer surface of such a tlieca, which is no 

 longer the outer surface of the prototheca. To the flesh thus 

 hanging- over Bourne's term " perlsarc" may be applied, and 

 lower down we will compare it with, and distinguish It from, 

 another principle of structure which also involves the forma- 

 tion of a perisarc. A calicle built up of a succession of such 

 protothecfe as those now under discussion, one fitted inside 

 the other, as in diagram fig. 1, would have a rib-like arrange- 

 ment of septa running down on the outside ; but in this case 

 one would expect to find traces of the hanging rims appearing 

 irregularly one above another as whole or portions of rings 

 round the corallum. They woukl appear to be drooping or 

 perhaps even show a tendency to curl up again. 



It is because no such epithecal rims show in the fig. 2, pi. 50, 

 ' British Fossil Corals,' that I doubt whether its prototheca 

 has this form (13 h) or belongs to the type I shall presently 

 describe as also depending upon the formation of a perisarc. 

 This point, then, may b3 left for the present. It is clear at 

 any rate that its true place Is nowhere among the Cyatho- 

 phyllid?e. 



This form 13 7i Is of special importance, however, for the 

 understanding It gives of the morphology of the Silurian 

 CalostjjUs as developed by Lindstrom. 



This coral has been announced as a Palaeozoic Perforate, 

 and this claim has had to be dealt with for the British 

 Museum Catalogue, the first section of which, it is proposed, 

 shall deal with the Perforata. As I have shown above, the 

 true Perforates were only possible when the prototheca was 

 flattened out as shown In diagram fig. 10. When thus flat- 

 tened the septal ridges towered up above it and free of its rim, 

 carrying on the skeleton by themselves alone. The thecai 

 being constructed solely of radial plates and their synapti- 

 culse were necessarily porous. In Calostylis the prototlieca 

 was not flattened out at all, but folded as shown in 13 h, and 

 the septa were not laminate, but appear to have been repre- 

 sented by a compact mass of large, irregular, rounded or 

 subangular nodules, arranged roughly in radial rows. These 

 come over the edge of the thecal fold and extend down to tho 



9^ 



